Ivanka Trump and Sen. Rob Portman, an Ohio Republican, during a bipartisan round table discussion on sex trafficking with members of Congress and the private sector, March 13, 2018, in Washington, DC.

The Stop Enabling Sex Trafficking Act (SESTA) was passed by Congress on Wednesday, and it’s already having an impact.

Craigslist took down its Personal Ads section Thursday night, saying the bill's passage opens it up to “criminal and civil liability when third parties (users) misuse online personals unlawfully,” and that it “can't take such risk without jeopardizing all our other services.”

RIP Craigslist personal ads. I said it earlier today, &amp; I am going to say it again. If you are are not gravely concerned about the horrifying censorship that is happening right now, you should be. This the the most frightening thing I've ever seen in terms of the Internet.

SESTA’s goal is to prevent sex trafficking, particularly child sex trafficking, by restricting what kind of information can be posted on websites like Backpage, where people often advertise sexual services. But the sex workers who use these sites, as well as organizations like the American Civil Liberties Union, say the broadly written bill actually endangers sex workers, and restricts freedom of speech.

Some groups, like the women’s rights group Equality Now, say that’s a good thing. “We will stand with survivors in holding companies that knowingly sell women and girls' bodies online for sex accountable under the law,” wrote director Shelby Quast in an email statement.

But because SESTA increases the risk of lawsuits, online platforms, especially the smaller ones, will likely be much stricter about what kind of content is on their sites. That’s why, at first, companies including Twitter, Google, Facebook, and Amazon tried to fight the bill, though eventually they gave in, according to the Washington Post. The turning point, according to the Internet Association, a lobbying organization that represents multiple tech companies, was changes to the the wording of the bill that would allow tech platforms to use automated methods for screening and deleting sex-trafficking content without implicating themselves, according to Motherboard. And because SESTA is intended to preventing child sex trafficking, it’s politically fraught for tech companies to oppose it.

Still, sex workers say that incentivizing tech companies to remove posts about sex work could endanger both their livelihood and their safety.

“With online advertising, people don't have to work on the street, go with strangers into their cars or unknown addresses,” Liara Roux, a sex worker and advocate, told BuzzFeed News via email. Roux argues that the SESTA language around “facilitating trafficking” is so broad that even the sites sex workers use to share information about bad clients or check in with each other could be included.

“Even recommending a friend to a safe client, or giving a reference to tell someone a client is safe could be considered facilitating,” she wrote.

SESTA critics not only argue that the law will make consensual sex work more difficult and dangerous, but could also make it harder to locate people who are actually victims of trafficking because online records give law enforcement a way to track victims.

Erika G, who wished to remain anonymous as she is not authorized to speak on behalf of her employer, is an attorney who works with trafficked women. On Twitter, she told the story of a client she was trying to help, who sometimes, due to lack of money, returned to sex work, missed legal appointments, and stopped communicating. Erika, who declined to share the name of the firm she works with, said that more than once she was only able to to find her client because her contact information was available on Backpage.

Once we were finally able to get her an ID she was able to stabilize and start working. Without Backpage I would have lost all contact with my client and she probably would not have been able to stabilize because of all the legal appointment she was missing.

Beyond the world of consensual sex work, there’s also concern that SESTA signals a broader weakening of laws meant to protect free speech online, and that the exemptions created for content that mentions sex trafficking could be applied to other types of speech. The Electronic Frontier Foundation called the bill “a win for censorship.”

The American Civil Liberties Union also actively fought against the bill.

“The risks to the Internet as the world’s most significant marketplace of ideas outweigh the uncertain benefit of the bill to the fight against sex trafficking,” wrote ACLU national political director Faiz Shakir in a letter addressed to the House of Representatives leadership. Despite amendments, Shakir wrote that the “ACLU remains concerned that the bill, if enacted, will foster an atmosphere of hesitation among online platform providers. This uncertainty will inhibit the continued growth of the Internet as a place of creativity and innovation.”

To win a lawsuit under SESTA, sex trafficking victims will have to prove that the website they’re suing “knowingly” facilitated the crime. What company or companies will be the first subject of such a suit remains to be seen.

It’s unknown when President Trump plans to sign the bill into law.

Caroline O'Donovan is a senior technology reporter for BuzzFeed News and is based in San Francisco.